refraction through prism experiment

Refraction of light through prism experiment

What happens when light goes through a prism? This is a great experiment demonstrating optical phenomenons like light dispersion, as well as the refraction of light through prism. High-quality glass prisms are not only great for teaching physics. They can also used for prism photography! Let’s now see how to use a prism to make a rainbow!

Table of Contents

What is light refraction?

In physics, light refraction is defined as an optical phenomenon by which the light is diverted when it penetrates another substance. For example, refraction occurs when a beam of light travels through the air before reaching the polished surface of a glass prism. In this example, the glass has a specific refractive index, which will determine the angle of the light deviation. Furthermore, the incidence angle of the light hitting the surface of the prism will also influence how the light is deviated.

What is light dispersion and how to use a prism to make a rainbow?

In addition to light refraction, another optical phenomenon is taking place within the prism. For instance, the prism experiment also demonstrate how light dispersion can happen. In short, the scientific principle behind it is that the refractive index of the prism depends on the wavelength of the light penetrating it. Therefore, if a beam of white light hits the prism, the various wavelengths corresponding to the full spectrum of colors composing the white beam will each be deviated at a specific angle. In other words, the white light will be separated into a colorful rainbow! This optical phenomenon is similar to the rainbows that you can see in the sky, in which water droplets are refracting the sunlight.

Check this Prism Ideal for Teaching Light Spectrum on Amazon

What is the relationship between color and wavelength for light?

The visible light spectrum is composed of several colors, each of them corresponding to a specific wavelength. Indeed, the human eye can perceive wavelengths ranging approximately from 390 to 700 nm. This range of wavelengths corresponds to the following colors, in this order:

Violet – Blue – Cyan – Green – Yellow – Orange – Red

On the other hand, the human eye will not see wavelengths outside the visible light spectrum. For instance, ultraviolet radiations are emitted at wavelengths below 390 nm and can’t be seen. This is also the reason why we can’t see infrared emissions at longer wavelengths.

How did newton prove that sunlight consists of many colors?

Looking at light through a prism is an idea that has been around for a long time. Indeed, both Descartes and Newton studied this optical phenomenon. In 1666, Newton enthusiastically wrote this in a letter:

“I procured me a Triangular glass prism, to try therewith the celebrated  Phœnomena  of  Colours … It was at first a very pleasant divertissement to view the vivid and intense colours produced” 1 .

During his career, Newton performed several experiments with prisms to study light refraction and dispersion. In one of his famous experiments, he cut a pinhole in is window shade to only allow the passage of a beam of sunlight. Using a glass prism, he demonstrated that the beam of light was refracted and changed its path, as he observed that its projection on a surface was diverted by the prism. He also noticed another optical phenomenon: light dispersion into a rainbow of colors! Using a second prism, he further proved that these various colors can be combined again to obtain white. As a result, he was able to prove that sunlight in fact consists of many colors.

Now you may be as thrilled as Newton to experiment light refraction and dispersion through a prism. You can easily find a small glass prism that will allow you to demonstrate the basic principles of physic optics. First, you can try to project the light beam towards a wall or other flat surface. You can also try different incidence angles and see how it affects the light emitted.

How to use a prism for photography?

There are many references to light refraction and dispersion in popular culture. Among the most iconic representation of this optical phenomenon is the cover of the album Dark side of the Moon by Pink Floyd.

Light refraction can also be used in photography. There are mainly two ways to use a prism. First, it can be employed to create a rainbow effect that can be incorporated within the picture. Some photographers also put a triangular glass prism in front of the objective to create a nice optical illusion. By doing this and by changing the angle of the prism, it is possible to capture a scene located in front of the objective while simultaneously incorporating elements perpendicular to the camera.

Click here to see where to buy a glass prism that can be used for photography

I hope you enjoyed reading this post about light refraction and dispersion through a prism. Before leaving, don’t forget to also have a look at my previous posts to learn about the camera obscura effect or the science behind optical microscopes .

1- https://royalsocietypublishing.org/doi/10.1098/rstl.1671.0072

2- https://en.wikipedia.org/wiki/Prism

3- https://en.wikipedia.org/wiki/Refraction

4- https://en.wikipedia.org/wiki/Color

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Refraction of Light Through a Prism | Science Experiment

by Cisco Ramon | Nov 30, 2021 | Experiments , Physics Experiments

Introduction

In this science experiment “Refraction of Light Through a Prism”, we shall learn to track the path of light rays through a prism.

A prism is a transparent, homogeneous glass enclosed by two inclined refracting surfaces at an angle called refracting angle. The refracting angle is also called the angle of prism.

1. Two triangular bases ABC and DEF, 2. Three rectangular lateral surfaces ADFC, ADEB and BCFE. 3. Six vertices A, B, C, D, E and F. 4. Nine edges AB, AC, BC, FD, DE, EF, AD, BE, and CF.

Important Points About Prism

1. Triangular prism is a refracting glass. 2. Angle of deviation is the angle between incident and ray and emergent ray. 3. Angle of deviation depends upon incident ray, angle of deviation and nature of prism. 4. Angle of incidence is inversely proportional to the angle of deviation, i.e. angle of incidence increases, the angle of deviation decreases. 5. The minimum angle of deviation of a prism is called minimum deviation. 6. Under this position (minimum deviation), refracted rays are parallel to the prism’s base. 7. The phenomenon of splitting white light into seven colours after refraction through a prism is called the dispersion of light.

To track the path of light rays through a prism.

Apparatus Required

1. A drawing board, 2. Drawing pins, 3. A prism, 4. Three white sheets, 5. Metre scale, 6. One pencil 7. One protector

Here, PQ = Incident ray QR = Refracted ray RS = Emergent ray MM’= Normal NN’= Normal <i = angle of incidence <r = angle of refraction <e = angle of emergence <A = angle of prism

1. On moving from denser medium to rarer medium, the light bends away from the normal while in moving from rarer to denser medium, it bends towards the normal. 2. The incident light ray PQ travel from a rarer medium to a denser medium (air to glass), it will bend towards the normal. 3. When the same light ray leaves the prism RS, it goes from a denser medium to a rarer medium. So it will bend away from normal.

1. With the help of some drawing pins, fix a white sheet on the drawing board. 2. Place the prism in the middle of the paper. 3. Draw its boundary with a pencil. Name it ABC. 4. Remove the prism. 5. Extend the line AB to XY, as shown in the figure. 6. Draw a normal NN’ perpendicular to AB. 7. Draw an incident angle <EFN = 30°. 8. Again, place the prism on the drawn boundary. 9. Fix two pins Pand Q on points E and F. 10. Now, fix two pins R and S, where the images of pins P and Q are obtained. 11. Fix two more pins such that feet of P1 and Q1 appear on the same straight line as of R and S. 12. Remove all pins and prism. Mark every point. 13. Join P1 and Q1 at G on the side AB. HG is the emergent ray. 14. Repeat this experiment by taking different values of incident angle such as 30°, 45°, 50°.

Observations

1. When a light ray enters from air to glass, it bends toward the normal, and when it leaves the prism, i.e. moving from glass to air, it turns away from the normal. 2. Therefore, the light ray undergoes two deviations in its path.

EFGH is the path taken by light rays.

Precautions

1. Prism should be thoroughly cleaned. 2. Pencil should be sharp for drawing boundaries. 3. Pins should be placed vertically. 4. The distance between two pins should be 6 cm. 5. The angle of incidence must be between 30° and 60°. 6. Arrows should be drawn to indicate the path of a light ray.

Sources Of Error

1. Pins may not lie on the same straight line. 2. Angle may not be taken accurately. 3. Pins can be bent. 4. Pins may not be pointed or sharped.

Additional Activity

To measure the angle of deviation.

1. Follow all the steps given above. 2. Draw a normal MM’ at G. 3. Produce EF to L and GH to O meeting at point J. 4. Measure <GJL as it is the angle of deviation. 5. Repeat this experiment by taking different values of incident angle such as 30°, 45°, 50°. 6. Draw a graph between the incident ray on the X-axis and the angle of deviation on the Y-axis.

Observation Table

1. Firstly angle of deviation decreases with an increase in incident angle, but after a certain point, it will increase with the increase in incident angle. 2. From the above observation, the minimum value of angle of deviation =………..°.

In this way, we have learnt to track the path of light rays through a prism.

Viva Questions With Answers

Q.1 What was the aim of our experiment? ANS.  To track the path of light rays through a prism.

Q.2 Describe prism? ANS. A prism is a transparent, homogeneous glass enclosed by two inclined refracting surfaces at an angle called refracting angle. The refracting angle is also called the angle of prism. It has- 1. Two triangular bases. 2. Three rectangular lateral surfaces. 3. Six vertices. 4. Nine edges.

Q.3 What do you mean by the angle of refraction? ANS. The angle between the normal and the incident ray is called the angle of reflection.

Q.4 Name the scientist who obtained spectrum from light rays? ANS. Sir Issac Newton.

Q.5 What do you mean by dispersion of light?

ANS. The phenomenon of splitting up white light into seven colours after refraction through a prism is called the dispersion of light.

Q.6 What is VIBGYOR? ANS. Violet, Indigo, Blue, Green, Yellow, Orange and Red.

Q.7 On what factors does the angle of deviation depends? ANS. 1. Incident angle, 2. Angle of a prism, 3. Nature of prism.

Q.8 What is the angle of refraction? ANS. The angle between the normal and the refracted ray is known as the angle of refraction.

Q.9 Name the property used by a prism to form a spectrum. ANS. Refraction of light.

Q.10 How many times does the light faces deviation in its path in a prism? ANS. Two

An Indian physicist and astronomer.

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In the Light and Color unit of The Physics Classroom Tutorial, the visible light spectrum was introduced and discussed. Visible light, also known as white light, consists of a collection of component colors. These colors are often observed as light passes through a triangular prism. Upon passage through the prism, the white light is separated into its component colors - red, orange, yellow, green, blue and violet. The separation of visible light into its different colors is known as dispersion . It was mentioned in the Light and Color unit that each color is characteristic of a distinct wave frequency; and different frequencies of light waves will bend varying amounts upon passage through a prism. In this unit, we will investigate the dispersion of light in more detail, pondering the reasons why different frequencies of light bend or refract different amounts when passing through the prism.

Earlier in this unit, the concept of optical density was introduced. Different materials are distinguished from each other by their different optical densities. The optical density is simply a measure of the tendency of a material to slow down light as it travels through it. As mentioned earlier, a light wave traveling through a transparent material interacts with the atoms of that material. When a light wave impinges upon an atom of the material, it is absorbed by that atom. The absorbed energy causes the electrons in the atom to vibrate. If the frequency of the light wave does not match the resonance frequency of the vibrating electrons, then the light will be reemitted by the atom at the same frequency at which it impinged upon it. The light wave then travels through the interatomic vacuum towards the next atom of the material. Once it impinges upon the next atom, the process of absorption and re-emission is repeated.  

The optical density of a material is the result of the tendency of the atoms of a material to maintain the absorbed energy of the light wave in the form of vibrating electrons before reemitting it as a new electromagnetic disturbance. Thus, while a light wave travels through a vacuum at a speed of c (3.00 x 10 8 m/s), it travels through a transparent material at speeds less than c . The index of refraction value ( n ) provides a quantitative expression of the optical density of a given medium. Materials with higher index of refraction values have a tendency to hold onto the absorbed light energy for greater lengths of time before reemitting it to the interatomic void. The more closely that the frequency of the light wave matches the resonant frequency of the electrons of the atoms of a material, the greater the optical density and the greater the index of refraction. A light wave would be slowed down to a greater extent when passing through such a material

The Angle of Deviation

Of course the discussion of the dispersion of light by triangular prisms begs the following question: Why doesn't a square or rectangular prism cause the dispersion of a narrow beam of white light? The short answer is that it does. The long answer is provided in the following discussion and illustrated by the diagram below.

Suppose that a flashlight could be covered with black paper with a slit across it so as to create a beam of white light. And suppose that the beam of white light with its component colors unseparated were directed at an angle towards the surface of a rectangular glass prism. As would be expected, the light would refract towards the normal upon entering the glass and away from the normal upon exiting the glass. But since the violet light has a shorter wavelength, it would refract more than the longer wavelength red light. The refraction of light at the entry location into the rectangular glass prism would cause a little separation of the white light. However, upon exiting the glass prism, the refraction takes place in the opposite direction. The light refracts away from the normal, with the violet light bending a bit more than the red light. Unlike the passage through the triangular prism with non-parallel sides, there is no overall angle of deviation for the various colors of white light. Both the red and the violet components of light are traveling in the same direction as they were traveling before entry into the prism. There is however a thin red fringe present on one end of the beam and thin violet fringe present on the opposite side of the beam. This fringe is evidence of dispersion. Because there is a different angle of deviation of the various components of white light after transmission across the first boundary, the violet is separated ever so slightly from the red. Upon transmission across the second boundary, the direction of refraction is reversed; yet because the violet light has traveled further downward when passing through the rectangle it is the primary color present in the lower edge of the beam. The same can be said for red light on the upper edge of the beam.

Dispersion of light provides evidence for the existence of a spectrum of wavelengths present in visible light. It is also the basis for understanding the formation of rainbows. Rainbow formation is the next topic of discussion in Lesson 4.

• The Anatomy of a Lens

NOTIFICATIONS

Refraction of light.

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Refraction is the bending of light (it also happens with sound, water and other waves) as it passes from one transparent substance into another.

This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows. Even our eyes depend upon this bending of light. Without refraction, we wouldn’t be able to focus light onto our retina.

Change of speed causes change of direction

Light refracts whenever it travels at an angle into a substance with a different refractive index (optical density).

This change of direction is caused by a change in speed. For example, when light travels from air into water, it slows down, causing it to continue to travel at a different angle or direction.

How much does light bend?

The amount of bending depends on two things:

• Change in speed – if a substance causes the light to speed up or slow down more, it will refract (bend) more.
• Angle of the incident ray – if the light is entering the substance at a greater angle, the amount of refraction will also be more noticeable. On the other hand, if the light is entering the new substance from straight on (at 90° to the surface), the light will still slow down, but it won’t change direction at all.

Refractive index of some transparent substances

All angles are measured from an imaginary line drawn at 90° to the surface of the two substances This line is drawn as a dotted line and is called the normal.

If light enters any substance with a higher refractive index (such as from air into glass) it slows down. The light bends towards the normal line.

If light travels enters into a substance with a lower refractive index (such as from water into air) it speeds up. The light bends away from the normal line.

A higher refractive index shows that light will slow down and change direction more as it enters the substance.

A lens is simply a curved block of glass or plastic. There are two kinds of lens.

A biconvex lens is thicker at the middle than it is at the edges. This is the kind of lens used for a magnifying glass. Parallel rays of light can be focused in to a focal point. A biconvex lens is called a converging lens.

A biconcave lens curves is thinner at the middle than it is at the edges. Light rays refract outwards (spread apart) as they enter the lens and again as they leave.

Refraction can create a spectrum

Isaac Newton performed a famous experiment using a triangular block of glass called a prism. He used sunlight shining in through his window to create a spectrum of colours on the opposite side of his room.

This experiment showed that white light is actually made of all the colours of the rainbow. These seven colours are remembered by the acronym ROY G BIV – red, orange, yellow, green, blue, indigo and violet.

Newton showed that each of these colours cannot be turned into other colours. He also showed that they can be recombined to make white light again.

The explanation for the colours separating out is that the light is made of waves. Red light has a longer wavelength than violet light. The refractive index for red light in glass is slightly different than for violet light. Violet light slows down even more than red light, so it is refracted at a slightly greater angle.

The refractive index of red light in glass is 1.513. The refractive index of violet light is 1.532. This slight difference is enough for the shorter wavelengths of light to be refracted more.

A rainbow is caused because each colour refracts at slightly different angles as it enters, reflects off the inside and then leaves each tiny drop of rain.

A rainbow is easy to create using a spray bottle and the sunshine. The centre of the circle of the rainbow will always be the shadow of your head on the ground.

The secondary rainbow that can sometimes be seen is caused by each ray of light reflecting twice on the inside of each droplet before it leaves. This second reflection causes the colours on the secondary rainbow to be reversed. Red is at the top for the primary rainbow, but in the secondary rainbow, red is at the bottom.

Activity ideas

Use these activities with your students to explore refration further:

• Investigating refraction and spearfishing – students aim spears at a model of a fish in a container of water. When they move their spears towards the fish, they miss!
• Angle of refraction calculator challenge – students choose two types of transparent substance. They then enter the angle of the incident ray in the spreadsheet calculator, and the angle of the refracted ray is calculated for them.
• Light and sight: true or false? – students participate in an interactive ‘true or false’ activity that highlights common alternative conceptions about light and sight. This activity can be done individually, in pairs or as a whole class .

Useful links

Learn more about different types of rainbows, how they are made and other atmospheric optical phenomena with this MetService blog and Science Kids post .

Learn more about human lenses, optics, photoreceptors and neural pathways that enable vision through this tutorial from Biology Online .

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• Refraction Light Glass Prism

Refraction of Light through a Glass Prism

Did you know that scientists today are very close to successfully inventing an invisibility cloak? If you think this is magic, you are wrong. The aim of these scientists is to make a fabric that will hide objects completely, at least in visible light. This is based on a fundamental scientific principle: the principle of refraction. According to this, light travels from one medium to another and changes its direction.

To learn about the refraction of light through a prism, see the video below

Phenomena Caused by Refraction:

Refraction is the cause of a lot more phenomena.

• When you look at a straw dipped in a glass of water, the part in the air and the part in the water look like they are not the same straw! It looks distorted.
• Sometimes, in a desert, travellers see water or trees on the ground when there is actually nothing there. This phenomenon is known as ‘mirage’.
• Some other natural phenomena also occur because of refraction, such as the twinkling of stars and the formation of rainbows.

A rainbow is formed when sunlight passes through water droplets and disperses into the 7 colours it is made up of. In fact, rainbow-like substances can be formed even when light passes through a prism. Due to the shape of a prism, dispersion of light can take place when it passes through it. To understand this, let’s understand how refraction occurs when light passes through a glass prism.

Revision of the chapter Human Eye and the Colourful World

All the concepts in the chapter Light: Light Reflection and Refraction

• If you take a glass prism, you can see that it has 2 triangular bases and three rectangular lateral surfaces inclined at an angle. This angle is called the angle of the prism.
• Let’s look at a top view of a triangular prism with a ray of light entering it.

In the figure above, A is the angle of the prism.

• As per Snell’s law, light travelling from a rarer medium to a denser medium bends towards the normal, and vice versa. Glass is denser than air, and thus, when a ray of light falls on the surface of the prism, it bends towards the normal. According to the diagram, ray PE falls on the surface of the prism and bends towards the normal NE.
• Then, while moving from the glass to the air, the emergent ray FS bends away from the normal.
• ∠HDS is the angle of deviation which tells us how much the emergent ray has deviated from the incident ray. When the angle of incidence is equal to the emergence angle, the deviation angle is minimum.
• According to the figure, ∠PEN = ∠MES and ∠HDS is thus the angle of minimum deviation. The refracted ray EF is parallel to side BC in this case.

This is how a ray of white light scatters into 7 colours when it passes through a prism. The different colours of light waves experience a different degree of deviation; thus, white light splits into its components when subjected to refraction.

Read More: Snell’s Law

The below videos help to revise the chapter Light Reflection and Refraction Class 10

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Dispersion Of Light Through A Prism

The story of light dispersion through a prism begins with the foundational work of Sir Isaac Newton in the 17th century. Newton was fascinated by the nature of light and its properties. His curiosity led to a series of experiments that would forever change our understanding of optics.

In 1666 , Newton conducted an experiment that was simple yet revolutionary. He allowed a beam of sunlight to pass through a triangular glass prism in a darkened room. To his surprise, instead of white light emerging from the other side, he observed a spectrum of colors.

Newton deduced that white light was not pure but a mixture of different colors. Each color had a different wavelength and bent by a different amount when passing through the prism. This bending, or refraction, caused the white light to spread out into a spectrum of colors, a phenomenon he named the dispersion of light .

Newton was meticulous and cautious about sharing his findings. It wasn’t until 1704 , after much persuasion, that he published his work in a book titled “Opticks”. In it, he detailed his experiments and theories on light, including the concept of dispersion. Newton’s work laid the groundwork for modern optics. His prism experiment was a pivotal moment in science, leading to the development of new optical instruments and enhancing our understanding of the nature of light.

Today, Newton’s insights into the dispersion of light continue to influence various fields, from spectroscopy to astronomy. His principles are taught worldwide, forming a fundamental part of physics education.

Table of Contents

What is the Dispersion of Light?

Dispersion of light is a fascinating and colorful phenomenon that occurs when white light is separated into its constituent colors. Dispersion of light is the separation of white light into its constituent colors when it passes through a medium like a prism. This occurs because different colors of light bend by different amounts due to their varying wavelengths.

Imagine white light as a team of runners, each wearing a different color shirt, racing through a medium like glass or water. As they run, they encounter a hurdle—the prism—which slows them down. But here’s the catch: each runner is slowed down by a different amount because of their unique shirt color, which represents the light’s wavelength.

In more scientific terms, dispersion happens because light is made up of waves, and these waves have different lengths. When white light enters a prism, each color of light is refracted, or bent, to a different degree. Violet light, with the shortest wavelength, is bent the most, and red light, with the longest wavelength, is bent the least. This separation of colors is what we call dispersion.

It’s like a musical band where each instrument plays a different note, and when they enter the prism, each note is directed to a different part of the room. The result is not just a single melody but a spectrum of musical notes spread across the space, similar to how light spreads across a spectrum of colors.

So, when we talk about the dispersion of light, we’re referring to this process of separating white light into a rainbow of colors. It’s a fundamental concept that explains why we see the colors we do and is essential for understanding the behavior of light as it travels through different mediums.

Dispersion of White Light by Glass Prism

The dispersion of white light by a glass prism occurs because different colors of light are refracted by different amounts due to their wavelengths. This results in the spread of white light into a continuous spectrum of colors, which we can observe as it exits the prism. When white light enters a glass prism, it refracts and splits into a spectrum of colors—red, orange, yellow, green, blue, indigo, and violet. Red light bends the least, while violet bends the most.

Imagine you have a beam of white light, like sunlight. This light contains all the colors of the rainbow, but you can’t see them because they’re all mixed. Now, let’s say you pass this white light through a triangular glass prism. What happens inside the prism is quite remarkable and is the essence of dispersion.

As the white light enters the prism, it encounters a change in medium from air to glass. This causes the light to slow down and bend—a process known as refraction. However, not all colors of light bend the same amount. Violet light, with its shorter wavelength, bends the most, and red light, with its longer wavelength, bends the least. This difference in bending causes the white light to spread out into a spectrum of colors.

Inside the prism, each color of light travels at a different speed because the glass prism has a different refractive index for each wavelength. This is why the colors separate: each one is refracted at a slightly different angle. When the colors emerge out of the prism, they have fanned out into a beautiful spectrum, displaying all the colors from violet to red.

This separation of colors is what we call the dispersion of white light. It’s a simple yet profound demonstration that white light is made up of a spectrum of colors, and it’s the glass prism that acts as the tool to reveal this hidden secret.

Factors Influencing Dispersion of Light:

Dispersion is the process where white light separates into its component colors. This happens when light passes through a medium like a prism. But what determines how much each color spreads out? That’s where the factors influencing dispersion come into play.

Refractive Index: The refractive index of a medium is a measure of how much it can bend light. Materials with a higher refractive index will bend light more, causing greater dispersion. Think of it like running on a track; if the track suddenly becomes softer, you’ll slow down more and your path will bend.

The wavelength of Light: The wavelength of light is another crucial factor. Colors with shorter wavelengths (like blue and violet) are dispersed more than colors with longer wavelengths (like red). It’s similar to how a small car can make sharper turns compared to a long bus.

The angle of Incidence: The angle of incidence is the angle at which light hits the prism. This angle affects how much the light is bent inside the prism. If the light enters at a steeper angle, the dispersion will be more pronounced, just as a ball hitting a wall at a sharp angle bounces off further away.

Material Composition: The material composition of the prism also plays a role. Different materials have different capacities to disperse light. For example, a diamond prism will disperse light more than a glass prism because of its unique internal structure.

Prism Shape: Lastly, the shape of the prism itself can influence dispersion. A prism with a more acute angle will spread the colors out more than a prism with a wider angle. This is because the light spends more time inside the prism, which increases the effect of dispersion.

By understanding these factors, students can get a clearer picture of why dispersion occurs and how it behaves under different conditions.

Refraction of Light through Prism

Refraction is the bending of light as it passes from one transparent medium into another. This happens because light travels at different speeds in different mediums.

When a beam of white light hits a glass prism, it enters from the air (a rarer medium) into a glass (a denser medium). As it enters the glass, the light slows down and bends towards the normal line—a line perpendicular to the surface at the point of contact.

Once inside the prism, the light continues to travel, bending further as it passes through the glass. The amount of bending depends on the angle of incidence (the angle at which the light hits the prism) and the material’s refractive index (a number that describes how much the material can bend light).

As the light exits the prism, it moves from the glass back into the air. It speeds up again and bends away from the normal line. This change in speed and direction is what causes the light to refract. The path that the light takes through the prism is not straight. Instead, it’s a zigzag path due to the bending at both the entry and exit points. The overall effect is that the light has changed direction from its original path—this change is the angle of deviation .

Light bends because it follows the law of refraction , also known as Snell’s Law . This law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant and is equal to the refractive index. Refraction of light through a prism is a process where light bends as it passes from one medium to another, changing speed due to the different optical densities. This bending is responsible for the path of light being altered as it travels through the prism.

Visible Light Spectrum

The visible light spectrum is the range of electromagnetic waves that we can see. Each color has a different wavelength, and together they make up the light that brightens our world and allows us to enjoy the beauty of a rainbow or a sunset. The visible light spectrum is the range of light wavelengths that the human eye can see, approximately from 380 nm (violet) to 750 nm (red).

The visible light spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. It consists of a range of wavelengths that we perceive as different colors. The spectrum includes the colors red, orange, yellow, green, blue, indigo, and violet.

Each color in the visible spectrum has a specific wavelength range:

Our eyes have receptors called cones that are sensitive to these wavelengths. When light enters our eyes, the cones translate these wavelengths into electrical signals that our brain interprets as colors. The visible spectrum is continuous, meaning there are no gaps between the colors. They blend seamlessly into one another, creating the full array of colors we can see. Just outside the visible spectrum are ultraviolet light, which has shorter wavelengths, and infrared light, which has longer wavelengths. These are not visible to the naked eye but can be detected with special instruments.

Angle of Deviation

The angle of deviation is the angle between the direction of the incoming light and the direction of the light as it exits the prism. Each color has a different angle of deviation due to its unique wavelength. The angle of deviation is a measure used in optics to describe how much a beam of light is bent, or deviated, as it passes through a prism.

Imagine a football player running straight towards a goal. If the player encounters an obstacle that makes them change direction, the angle between their original path and their new path is similar to the angle of deviation in light. The greater the obstacle’s influence, the larger the deviation.

In technical terms, the angle of deviation (usually denoted by the Greek letter \(\displaystyle\delta \)) is the angle made between the incident ray of light entering the first face of the prism and the refracted ray that emerges from the second face of the prism. It’s like measuring the change in direction from where the light first hits the prism to where it comes out on the other side.

The angle of deviation is important because it tells us how much each color of light is bent by the prism. Since different colors of light have different wavelengths, they are deviated by different amounts. Violet light, for example, is bent more than red light.

The reason for this difference in bending is due to the light’s wavelength. Shorter wavelengths (like violet) are bent more, and longer wavelengths (like red) are bent less. This is why we see a spectrum of colors when white light passes through a prism – each color is deviated at a slightly different angle.

The exact angle of deviation depends on the prism’s material and the wavelength of light. It can be calculated using Snell’s Law and the prism’s geometry. For a simple glass prism, the formula to find the angle of deviation for a particular wavelength involves the refractive index of the material and the angle at which the light enters the prism.

The Angle of Deviation for White Light through a Prism:

The angle of deviation is the measure of how much a ray of light has been bent from its original path after passing through a prism. For white light, which is a mix of all visible colors, each color deviates by a different amount because each color has a different wavelength.

When white light enters a prism, it’s like a group of athletes, each running at a different speed, entering a field with a barrier. The athletes represent different colors of light, and the barrier represents the prism. As they cross the barrier, each one changes direction slightly. The amount they change direction, or their angle of deviation, depends on their speed, just like it depends on the wavelength of light.

Violet light, with the shortest wavelength, is bent the most, while red light, with the longest wavelength, is bent the least. This spread of colors is what creates a spectrum. The angle of deviation is largest for violet and smallest for red, with all the other colors falling in between.

The shape of the prism also affects the angle of deviation. A triangular prism with non-parallel sides will cause an overall angle of deviation for the various colors of white light, spreading them out to form a spectrum. The exact angle of deviation for each color can be calculated using Snell’s Law and the geometry of the prism.

Interestingly, there is a particular angle at which the light enters the prism where the deviation is the smallest for all colors. This is known as the angle of minimum deviation, and it occurs when the light travels symmetrically through the prism, with the path inside the prism being parallel to the base. This angle is unique for each color due to their different wavelengths.

The angle of deviation for white light through a prism is a beautiful demonstration of how light’s inherent properties, combined with the geometry of the prism, can lead to the colorful display we know as the spectrum.

Newton’s Prism Experiment

Sir Isaac Newton’s prism experiment was a pivotal moment in the scientific study of light and color. In 1666, Newton conducted a series of experiments to delve into the nature of light. Newton’s experiment showed that a prism could decompose white light into a spectrum of colors and that these colors could be recombined to form white light again.

Newton darkened his room and made a small hole in his window shutter, allowing just a single beam of sunlight to enter. He then placed a triangular glass prism in the path of the sunlight. As the sunlight passed through the prism, it spread out into a band of colors on the opposite wall. This band, known as a spectrum, displayed all the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet.

Newton observed that the prism did not create the colors; rather, it separated the colors that were already present in the sunlight. He realized that white light is a mixture of all the colors of the visible spectrum. To confirm his hypothesis, Newton performed another experiment. He placed a second prism upside down in front of the spectrum created by the first prism. Instead of creating a new set of colors, the second prism recombined the spectrum back into white light.

Newton concluded that white light is composed of different colors, and these colors can be separated and recombined by refraction through prisms. His experiment fundamentally changed our understanding of light and laid the foundation for the field of optics. Newton’s experiment with prisms showed that light is a complex entity made up of various colors, which can be bent and separated by refraction. This experiment is a classic example of how simple observations can lead to profound scientific discoveries.

Also Read: Total Internal Reflection

Some Natural Phenomena Due to Sunlight

A rainbow is a perfect example of light dispersion that we can observe in the sky. It occurs when sunlight interacts with raindrops after a storm. When sunlight enters a raindrop, it slows down and bends—a process known as refraction. Because sunlight is made up of different colors, each color bends at a slightly different angle due to its unique wavelength. Violet light bends the most, and red light bends the least.

A rainbow is a spectacular example of sunlight being dispersed by water droplets in the atmosphere. This phenomenon occurs due to the combined effects of dispersion, refraction, and reflection of sunlight by the spherical water droplets of rain.

Conditions for Observing a Rainbow: The Sun must be shining in one part of the sky, for example, near the western horizon. It should be raining in the opposite part of the sky, such as the eastern horizon. An observer can only see a rainbow with their back facing the Sun.

Figure (a) helps us understand the steps involved in the formation of a rainbow: When sunlight enters a raindrop, it is refracted (bent). This refraction causes the different wavelengths (colors) of white light to spread out. Longer wavelengths like red are bent the least, while shorter wavelengths like violet are bent the most.

These separated colors then strike the inner surface of the water droplet. If the angle of incidence is greater than the critical angle (48° for water), the light undergoes internal reflection.

The reflected light exits the droplet, undergoing another refraction. This further separates the colors. For example, violet light exits the raindrop at an angle of 40° relative to the incoming sunlight, and red light exits at an angle of 42°. Other colors emerge at angles between these two values.

Figure (b) shows how a primary rainbow forms: Red light from one droplet (drop 1) and violet light from another droplet (drop 2) reach the observer’s eye. Violet light from drop 1 and red light from drop 2 are directed above or below the observer.

The observer sees a rainbow with red on the top and violet on the bottom because of the angles at which these colors emerge from the droplets. The primary rainbow results from a three-step process: refraction, reflection, and refraction.

Figure (c) explains the formation of a secondary rainbow: A secondary rainbow occurs when light undergoes two internal reflections inside a raindrop instead of one. The secondary rainbow is fainter because some light intensity is lost during the second reflection. The order of colors is reversed compared to the primary rainbow, with red on the inner edge and violet on the outer edge.

The arc shape of a rainbow is due to the angle at which the sunlight is refracted and then reflected inside the raindrops. The light that reaches your eyes from the higher raindrops appears red, while the light from the lower raindrops appears violet, with all the other colors in between.

The colors of a rainbow always appear in the same order: red, orange, yellow, green, blue, indigo, and violet. This sequence is determined by the wavelengths of the colors, with red having the longest wavelength and violet the shortest.

Scattering Of Light

Scattering of light occurs when light rays encounter small particles in the atmosphere, such as air molecules, dust, or water droplets. These particles cause the light to change direction and spread out. During sunset and sunrise, the sun is near the horizon, and sunlight travels through a longer path in the atmosphere. This longer journey means the light encounters more particles, leading to more scattering.

The phenomenon responsible for the scattering of light in the atmosphere is known as Rayleigh scattering . It’s more effective at shorter wavelengths, such as blue and violet light, which is why the sky appears blue during the day. However, at sunrise and sunset, the situation is a bit different.

As the sun’s position is low, the sunlight’s path through the atmosphere is the longest. The blue and violet light is scattered out of the direct line of sight, and the longer wavelengths like red, orange, and yellow are less affected by scattering. This is why we often see a reddish sky at these times—the light that reaches us directly has more of the longer wavelengths.

Rayleigh’s law quantitatively describes the scattering of light, stating that the intensity of scattered light is inversely proportional to the fourth power of the wavelength. This means shorter wavelengths scatter much more than longer ones.

When light encounters particles in the atmosphere, it can be scattered. The nature of this scattering depends on the size of the particles relative to the wavelength of the light. The key factor here is the size of the particle (denoted as (a) compared to the wavelength of light (denoted as (λ). When the particles are much smaller than the wavelength of light (a << λ), we observe Rayleigh scattering .

Rayleigh scattering is more effective at shorter wavelengths. This is why the sky appears blue during the day; shorter (blue) wavelengths are scattered more than longer (red) wavelengths. The intensity of the scattered light (I) is inversely proportional to the fourth power of the wavelength (λ), which can be expressed as:

\(\displaystyle I \propto \frac{1}{\lambda^4} \)

For larger particles, such as dust and water droplets, the scattering is different. These particles are closer in size to the wavelength of visible light or even larger. In such cases, the scattering is less wavelength-dependent and can scatter light of all colors more or less equally. This is why clouds, which consist of water droplets, appear white; they scatter all wavelengths of light similarly.

Example: At sunset, sunlight travels through more of the Earth’s atmosphere, increasing the distance light travels through air and the number of particles it encounters. The increased scattering of shorter wavelengths of light (blue and violet) out of the line of sight leaves the longer wavelengths (red, orange, yellow) to reach the observer’s eyes, leading to the beautiful reds and oranges of a sunset.

The scattering of light in the atmosphere can vary depending on the size of the atmospheric particles relative to the wavelength of light. Rayleigh scattering dominates when the particles are much smaller than the wavelength, leading to the blue sky we see during the day, while larger particles scatter light more uniformly, contributing to the white appearance of clouds and the colors of sunsets.

Examples of Dispersion of Light

Rainbows : A rainbow is one of the most beautiful natural examples of light dispersion. After it rains, sunlight shines into droplets of water left in the air. Each droplet acts like a tiny prism, dispersing the sunlight into a spectrum of colors that arc across the sky.

Prisms : When white light passes through a glass prism , it is dispersed into a spectrum of colors. This happens because the different wavelengths of light are refracted by different amounts as they pass through the prism, separating the light into its constituent colors.

Soap Bubbles : The colorful patterns on soap bubbles are caused by dispersion. Light reflects off the different layers of soap film, and the varying thickness of the film causes different colors to be seen due to the dispersion of light.

CDs and DVDs : The surface of a CD or DVD can act like a prism. When light hits the surface, it’s dispersed into a rainbow of colors. This is due to the microscopic grooves on the disc diffracting the light and creating a spectrum.

Oil on Water : A thin layer of oil on water can create a rainbow effect. The light is dispersed by the varying thickness of the oil, which acts like a prism, separating the light into different colors.

These examples show how the dispersion of light is not just a concept in textbooks but a phenomenon that surrounds us, adding color to the natural world. It’s a principle that explains why we see such a variety of colors in different situations and helps students understand the practical implications of the theories they learn in class.

Practical Applications of Dispersion of Light

The dispersion of light, the process in which white light separates into its component colors, has several practical applications that are fascinating and integral to our daily lives. Here are some key applications explained simply:

• Spectroscopy: Spectroscopy is a technique that uses the dispersion of light to analyze the composition of materials. Scientists can identify the substance’s chemical makeup by passing light through a substance and examining the spectrum of colors produced.
• Optical Instruments: Prisms are used in various optical instruments like spectrometers and telescopes to disperse light into its constituent colors. This dispersion is crucial for understanding the properties of light from different celestial bodies.
• Vision Correction: Prism spectacles utilize dispersion to correct certain vision problems. These glasses have prisms that adjust the light entering the eyes, helping to correct alignment issues and improve visual clarity.
• Laser Tuning: In laser technology, dispersion is used to tune lasers to emit specific colors or wavelengths. This is essential in applications ranging from medical treatments to data transmission.
• Rainbow Formation: The natural phenomenon of rainbows is an example of dispersion. Sunlight disperses through water droplets in the atmosphere, creating the colorful arc we see in the sky after rain.
• Art and Decoration: The colorful patterns seen on CDs, soap bubbles, or oil spills on water are due to the dispersion of light. These effects are often used for artistic purposes or in decorative items.
• Environmental Monitoring: Dispersion can also be used to monitor environmental changes. For instance, changes in the dispersion patterns of sunlight can indicate the presence of pollutants in the atmosphere.

These applications show how the fundamental concept of light dispersion is applied in various fields, enhancing our scientific understanding and contributing to practical solutions in everyday life.

Also Read: Refraction Through A Prism

Q: What happens if you use a material other than glass for the prism?

When a material other than glass is used for a prism, the dispersion of light—that is, the separation of white light into its constituent colors—can vary significantly. This variation is primarily due to differences in the material’s optical density and refractive index, which are key factors in how much light bends when passing through the prism.

The optical density of a material is a measure of how much it slows down light. A material with a higher optical density will slow down light more, leading to a greater bending or refraction of the light rays. This means that materials with higher optical densities will generally cause more dispersion.

The refractive index is a number that describes how much a material can bend light. It varies with the wavelength or color of the light, a phenomenon known as dispersion . Materials with higher refractive indices will disperse light more than those with lower refractive indices. For example, a diamond has a higher refractive index than glass and thus will disperse light into a more vivid spectrum.

Different materials will produce different dispersion characteristics. For instance:

• Diamond : Known for its high dispersion, resulting in a very colorful spectrum.
• Flint Glass : Has a higher dispersion than standard crown glass, leading to a wider spectrum.
• Acrylic : Typically has a lower refractive index than glass so it would produce less dispersion.

The spectrum quality produced by a prism also depends on the material. Some materials may produce a sharper, more defined spectrum, while others might result in a more blurred or less distinct spectrum.

The choice of material for a prism is often based on the desired application. For broad-spectrum spectroscopy, where a wide range of wavelengths needs to be covered, materials that provide good dispersion without too much absorption are preferred.

Using different materials for prisms affects the degree and quality of light dispersion. The choice of material will depend on the specific needs of the application, such as the required precision of the spectral lines and the range of wavelengths to be analyzed.

Q: Can you explain the concept of critical angle in non-glass prisms?

The critical angle is the angle of incidence above which light is internally reflected within a material. When light travels from a denser medium to a rarer medium (like from water to air), there’s a specific angle of incidence at which the refracted ray of light skims the surface. This specific angle is known as the critical angle.

For non-glass prisms, such as those made of water, acrylic, or diamond, the critical angle will differ because each material has a unique refractive index. The refractive indices of the two media at the interface determine the critical angle.

The critical angle (θ c ) can be calculated using Snell’s Law, which relates the angle of incidence (θ i ) to the angle of refraction (θ r ). The formula for the critical angle is:

\(\displaystyle \theta_c = \sin^{-1}\left(\frac{n_r}{n_i}\right) \)

where (n i ) is the refractive index of the denser medium (inside the prism) and (n r ) is the refractive index of the rarer medium (outside the prism).

For example, if you have a prism made of water (with a refractive index of about 1.33) in air (with a refractive index of about 1.00), the critical angle can be calculated as:

\(\displaystyle \theta_c = \sin^{-1}\left(\frac{1.00}{1.33}\right) \)

which gives a critical angle of about 48.6 degrees. Any light hitting the water-air interface at an angle greater than 48.6 degrees will be internally reflected.

The critical angle is a fundamental concept in optics that depends on the refractive indices of the materials involved. It’s the angle beyond which light cannot pass through the interface but is instead reflected into the material, and it varies for different materials used in prisms.

Q: How does dispersion change with irregular-shaped prisms?

Dispersion of light in irregular-shaped prisms can be quite different from what we observe in regular triangular prisms. In a regular prism, the path of light is predictable, with light entering and exiting at specific angles. In an irregular-shaped prism, the angles can vary greatly, leading to a more complex path for the light as it travels through the prism.

The angle of refraction, which is the angle at which light bends when entering or exiting the prism, can differ significantly in irregular shapes. This means that the angle of deviation for each color of light could be less uniform compared to a triangular prism.

The spread of the spectrum can also be affected. In a triangular prism, the spectrum is usually linear and orderly. In an irregular-shaped prism, the spectrum could be spread out in a non-linear fashion, potentially creating a more scattered pattern of colors. Due to the varying angles and surfaces, some colors may overlap or mix, leading to a less distinct separation of the spectrum. This can result in a blending of colors rather than a clear division between them.

The intensity of the dispersed colors might also change. Some colors may appear brighter or more pronounced, while others could be less visible, depending on the shape of the prism and how it affects the light’s path. Irregular shapes can cause light to pass through varying thicknesses of the prism material, which can alter the refractive index experienced by different light rays. This can further influence the dispersion pattern.

A regular prism produces a predictable and orderly spectrum, an irregular-shaped prism can create a more complex and less predictable pattern of dispersed light. The exact nature of the dispersion will depend on the specific shape and material of the prism.

Q: How does the angle of deviation change with different prism shapes?

The angle of deviation changes with different prism shapes due to the varying angles at which light enters and exits the prism, and the path it takes through the material. Here’s how different shapes influence the angle of deviation:

• Triangular Prisms : For a triangular prism, which is the most common type used to demonstrate dispersion, the angle of deviation depends on the refractive index of the material and the prism’s apex angle. The apex angle is the angle between the two faces of the prism through which light enters and exits. A larger apex angle generally results in a larger angle of deviation because the light spends more time inside the prism, increasing the opportunity for refraction.
• Rectangular Prisms : Rectangular prisms can also cause deviation of light, but since the angles at which light enters and exits are usually 90 degrees, there is no dispersion, and the deviation is minimal. The light path is essentially parallel-shifted.
• Pentagonal Prisms : Pentagonal prisms have more faces, which means that light can undergo multiple refractions. This can lead to a complex path of light within the prism, potentially increasing the angle of deviation depending on the arrangement of the faces.
• Prism Material : The material of the prism also affects the angle of deviation. Different materials have different refractive indices, which means that the same shape of prism made from different materials will deviate light by different amounts.
• The angle of Incidence : The angle at which light enters the prism, known as the angle of incidence, also plays a significant role. If the light enters at a steeper angle relative to the prism’s surface, the angle of deviation will be larger.

So, the angle of deviation is influenced by the shape of the prism, the material’s refractive index, and the angle of incidence. Each of these factors can alter the path of light through the prism, resulting in different angles of deviation for different prism shapes

What is the dispersion of white light by a glass prism and why does it occur?

Dispersion of white light by a glass prism occurs when white light passes through the prism and splits into its constituent colors. This happens because different colors (wavelengths) of light refract by different amounts as they pass through the prism. The variation in the refractive index for different wavelengths causes this separation, with violet light bending the most and red light bending the least.

What is the visible light spectrum, and what are its primary colors?

The visible light spectrum is the range of electromagnetic waves that are visible to the human eye, typically ranging from approximately 400 nm (violet) to 700 nm (red). The primary colors in the visible spectrum, in order of increasing wavelength, are violet, indigo, blue, green, yellow, orange, and red.

What was Newton’s prism experiment and what did it demonstrate about light?

Newton’s prism experiment involved passing a beam of sunlight through a glass prism, which resulted in the dispersion of light into a spectrum of colors. He further demonstrated that by passing the dispersed light through a second prism, the colors could be recombined to form white light again. This experiment proved that white light is composed of multiple colors and that prisms can separate and recombine these colors through refraction.

How are rainbows formed, and what role does dispersion play in their formation?

Rainbows are formed when sunlight passes through raindrops in the atmosphere. Each raindrop acts like a prism, refracting and internally reflecting the light, which then exits the drop and disperses into its constituent colors. The dispersion of light within the raindrop separates the colors, creating the circular spectrum observed in a rainbow.

What causes the scattering of light and why is the sky blue?

The scattering of light is caused by the interaction of light with small particles in the atmosphere. Shorter wavelengths of light (blue and violet) are scattered more than longer wavelengths (red and orange). Although violet light is scattered more, our eyes are more sensitive to blue light, and some violet light is absorbed by the upper atmosphere, making the sky appear blue during the day.

What is the phenomenon of a double rainbow and how does it occur?

A double rainbow occurs when light is reflected twice inside raindrops before emerging. The second reflection causes the formation of a secondary rainbow with colors reversed and appearing outside the primary rainbow. This secondary bow is usually fainter due to the extra reflection reducing the intensity of the light.

How does the scattering of light explain the reddish color of the sunset?

The reddish color of the sunset is explained by Rayleigh scattering. During sunset, the sun’s light has to pass through a greater thickness of the Earth’s atmosphere, which scatters shorter wavelengths (blue and violet) out of the direct path. This leaves the longer wavelengths (red and orange) to dominate the sky’s color, creating a reddish appearance at sunset.

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Refraction Through a Prism

Have you ever observed that the people standing in the pool always look shorter then they are? Also, the spoon in the glass of water appears to be bent. Why does this happen? This is because of refraction. Let us now study about ”refraction through a prism”.

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What is refraction.

Before studying how refraction takes place through a prism, let us see what refraction is. The change in direction or bending of a light wave passing from one transparent medium to another caused by the change in wave’s speed is the refraction. The extent of bending of light rays entering from one medium to another is the refractive index and is denoted by the ‘n’.

It is represented as n = c/v, where c = velocity/speed of light of a certain wavelength in the air and v = velocity of light in any medium.

Browse more Topics under Ray Optics And Optical Instruments

• Some Natural Phenomenon due to Sunlight
• Total Internal Reflection
• Reflection of Light by Spherical Mirrors
• Refraction at Spherical Surfaces and by Lenses
• Dispersion by a Prism
• Optical Instruments

What is a Prism?

It is a solid figure having two triangular bases and three rectangular surfaces and is the closed surface. The angle between each surface is the angle of the prism. Here the opposite surfaces are equal surfaces and are parallel.  We notice that here there are two refracting surfaces which means the surface where refraction of light takes place.

Learn more about Human eye and Defects of Vision here .

Let A, B, C be the glass of the prism. Suppose BC is the base and AB and AC are its two refracting surfaces. From the above figure, we can say that OP is the incident. The ray traveling through the rarer medium and than the refractive index of the prism is the incident ray. As the ray PQ strikes the surface of the and it is called as the  refracted ray . OR is the emergent ray which comes out.

When the ray light enters the glass, it bends towards normal and when ray comes out, it bends away from the normal. Now the angle between the emergent ray and incident ray is the angle of deviation. For a single refracting surface,  δ = |i – r|

In this case, δ = (i 1 + i 2 ) – (r 1 + r 2 )

δ = i 1  + i 2 – A, A is the angle between the prism between two lateral surfaces. We know that ∠A and ∠Q is 180º and Angle of the prism of (A) is r 1 + r 2

r 1   is the angle of refraction inside the prism and r 2  is the angle of refraction outside it. For an angle of minimum deviation, δ is minimum and i 1 = i 2 = i

δ min  = 2i – A

For small A, δ = (µ – 1) A

Minimum Angle of Deviation for a Prism

At the minimum deviation, Dm the refracted ray inside the prism becomes parallel to its base, i.e. i = e ⇒ r1 = r2 = r, then r = A/2 and Dm = 2i – A, where i is the angle of emergence, r1 and r2 are the angles of refraction and A is the angle of the prism.

Learn more about Atmospheric Refraction and Scattering of Light here .

Question For You

Q. A prism made up of flint glass is such that the incident ray does not emerge from the second surface. The critical angle for flint glass is 36º. Then, refracting angle A must be

Answer: D. In the prism to occur the total internal reflection, the reflecting angle must be more than twice the critical angle of the material. So here the critical angle for flint glass is 36º so the refracting angle must be greater than 72.

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Ray Optics and Optical Instruments

• Lambert’s Cosine Law
• Kaleidoscope
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Prism Simulation

What is a prism, what is refraction, what is refractive index, why does white light split when it passes through a prism, related simpop simulations:.

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Core Practical: Investigating Refraction ( Edexcel IGCSE Physics )

Revision note.

Core practical 4: investigating refraction

Aim of the experiment.

• To review your understanding of refraction use the revision note Reflection & refraction
• Independent variable = shape of the block
• Dependent variable = direction of refraction
• Width of the light beam
• Same frequency / wavelength of the light

Equipment list

• Protractor = 1°
• Ruler = 1 mm

Refraction experiment set up

Apparatus to investigate refraction

• Place the glass block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
• Switch on the ray box and direct a beam of light at the side face of the block
• A point on the ray close to the ray box
• The point where the ray enters the block
• The point where the ray exits the block
• A point on the exit light ray which is a distance of about 5 cm away from the block
• Draw a dashed line normal (at right angles) to the outline of the block where the points are
• Remove the block and join the points marked with three straight lines
• Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
• Repeat the procedure for each shape of perspex block (prism and semi-circular)
• Consider the light paths through the different-shaped blocks

Refraction experiment results with different media

Refraction of light through different shapes of perspex blocks

• The final diagram for each shape will include multiple light ray paths for the different angles of incidences ( i ) at which the light strikes the blocks
• Label these paths clearly with (1) (2) (3) or A , B , C to make these clearer 
• You can use the revision note Reflection & refraction to do this

Evaluating the experiment

Systematic Errors:

• Use a set square to draw perpendicular lines

Random Errors:

• Use a sharpened pencil and mark in the middle of the beam
• Use a protractor with a higher resolution

Safety considerations

• Run burns under cold running water for at least five minutes
• Avoid looking directly at the light
• Stand behind the ray box during the experiment
• Keep all liquids away from the electrical equipment and paper

You may be asked questions on how to perform this refraction experiment in your exam. You may also be required to complete a table of results or deduce the path of a refracted ray. 

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